Gasoline manufacture



Oct.' l4, 1941.'

E. W. THIELE GASOLINE MANUFACTURE Filed Feb. 5, 1938 Patented Oct. 14,1941 GASOLINE MANUFACTURE Ernest W. Thiele, Chicago, Ill., assignor toStandard Oil Company, Chicago, Ill., a corporation of IndianaApplication February 5, 1938, Serial lNo. 188,844

' (or. 19e-49) 2 Claims.

This invention relates to the manufacture of gasoline and moreparticularly to the manufacture of gasoline by a combination crackingprocess.

It is an object of this invention to provide a new and improved methodof gasoline manubination cracking process involving both thermal.

and catalytic cracking. Another object of the present invention is toprovide a combination cracking process in which cycle stock made from aviscosity breaker operation is utilized as a feed for a catalyticcracking operation. A still further `object of this invention is toprovide a combination cracking process involving catalytic cracking,thermal cracking and thermal viscosity lbreaking and in which theseoperations are combined in such manner as to produce larger yields ofimproved gasoline and to minimize operating dificulties. Other and stillfurther objects, uses, and advantages of my invention will becomeapparent as the description thereof proceeds.

The invention will be described in detail in connection with a specificembodiment thereof shown in the accompanying drawing which formsa por..tion of this specification and is to be read in connection therewith.The drawing is in simplied flow diagram form.

Referring more specifically to the drawing, heated crude oil from asource not shown enters crude flash tower I through line 2. From crudeflash tower I light naphtha together with any excess of normally gaseoushydrocarbons passes overhead through line 3 while a heavy naphtha whichserves as a reformer stock is removed by means of trap-out plate 4through line 5, and virgin gas oilis removed by means of trap-out plate`Ii through line 1. Materials heavier than gas oil are removed from thebase of tower I as a residuum through valve 8.

.Returning to the light naphtha and gases which pass overhead throughline 3, these pass through condenser 9 into reflux drum I0. Uncondensedgases from this reflux drum are taken overhead through valve .II andultimately enter stabilizer I2. The condensatefrom reflux drum I isremoved from the base thereof through pump I3 and a portion is returnedto the top of tower I as reflux by means of valve .I4 and line I5. Theremainder is taken through valve I6 and line I1 to storage or furthertreatment and constitutes the straight run gasoline portion of theproduct.

The heavy naphtha or reformer stock removed by means of trap-out plate 4may suitably have an initial boiling point between about 150 F. andabout'250" F. and a maximum boiling point between about 300 F. and about450 F. This material passes through valve I8V and lines I9 and 20,

ultimately entering the coils of thermal cracking furnace 2l. As will beseen hereinafter, the feed to this thermal cracking furnace preferablyin cludes cycle stocks from the catalytic cracking and thermal crackingoperations as well as the virgin reformer stock to which reference hasbeen made above. v

Gas oil which is removed from tower I by means of trap-out plate 6 maysuitably have an initial boiling point of, from about 350 F to about 525F. and a nal boiling point of from about 575 F. to about 800 F. Itpasses through valve Z2, line 23, and pump 24, and then through'thecoils of catalytic cracking furnace 25. As will be seen hereinafter,thejeed to this catalytic cracking furnace preferably includes cyclestock from a thermal viscosity breaker operation imaddition to thevirgin gas oil to which reference has just been made. l

Residuum from the base of crude flash tower I passes through valve 8,line 26, and pump 2l to the coils of thermal viscosity breaker yfurnace23.

Returning to furnace 25 the heated material passes overhead throughtransfer line 29 into catalyst chamber 30. It will be understood that inactual practice a number of catalyst chambers will usually be employedeither in series or in parallel and that means will be provided for theregeneration of the catalyst. Since, however, the present invention doesnot reside in s uch details, the catalyst portion of the operation hasbeen shown in the simplest diagrammatic fashion. Various catalysts lcanbe used in this catalyst chamber. It is preferred` however, to employ acatalyst of the argillaceous type. Clays, acid treated clay, fullersearth, diatomaceous earth,

. bauxite or the like can be used. Various metal oxides and combinationsof metal oxides can be employed.l Synthetic clays, for' instancealuminum silicate, are particularly suitable.

It is appropriate at this point to mention the conditions which maysuitably prevail in the three cracking zones to which reference has beenmade. The conditions prevailing in catalyst chamber 30 being cracked,the results which are desired and particularly upon Ithe catalystemployed. Moreover, the optimum temperature will depend to some extenton the pressure employed and both are inter-related with contact time.However, the

catalytic cracking operation can suitably be conducted at aboutatmospheric pressure or at other pressures ranging from somewhat lessthan atmospheric to about 100 pounds per square inch.` 5

Temperatures ranging from about 750 F. to about 1050 F. can be used.Preferably, however, temperatures ranging from about 800 F. to about 975F. are employed. For instance, the conditions in the catalytic chambercan be atmospheric pressure and about 900 F.

In the case of thermal cracking furnace 2| the outlet temperature cansuitably range from about 875 F. to about 1100 F. but preferably fromabout 900 F. to about 1020 F., for instance 940` 15 F., and the outletpressure can suitably rangeY from about 100 poundsper square inch toabout 1500 pounds per square inch, for instance 700 pounds per squareinch.

The outlet or transfer line temperature in the 20 case of viscositybreaker furnace 28 should in general be substantially lower than theoutlet or transfer line temperature in the case of thermal crackingfurnace 2|. The outlet temperature in the case of furnace 28 can, forinstance, range- 25 frcm about 825 F. to aboutv975 F., for instance 875F.- The corresponding pressure can suitably range from about A100 poundsper square inch to about 1000 pounds per square inch, for instance v200pounds per square inch. 30

Returning to catalyst chamber 38, the cracked material from this chamberpasses through line 3| into evaporator 32 which is shown integral withbubble tower 33 and separated therefrom by trap-out plate 34. From thebase of evapora- 35 tor 32 a tar or heavy fraction may be removedthrough valved line 35.

All material lighter'than tar passes overhead from evaporator 32 throughtrap-out plate 34 intobubble tower 33. From the base of bubble tower 33,i. e. from trap-out plate 34, a gas oil cycle lstock is removed by meansof valved line 36 and passes through line 20 and pump 31, and thencethrough the coils of furnace 2|.

It will be noted that furnace 2| voperates both 45 on a cycle stock fromthe catalytic cracking operation and on a lighter reformer stock of avirgin nature. It will further become apparent as the ldescriptionproceeds that a gas oil cycle stock from the thermal cracking operationitself is` recycled to the coils of furnace 2|.' It is a general rulethat, for a given degree of cracking, stocks which have already beencracked once require higher temperatures than do virgin stocks. Ontheother hand, it is also a rule that light charging stocks require highertemperatures than heavy charging stocks. For this reason it isparticularly appropriate to cycle a light virgin reformer stock, such asthat removed from trap-out plate 4 of tower I, together with heavier 60cracked cycle stocks to a single cracking operation, such as thatconducted in furnace 2|', since the optimum conditions are approximatelythe same for the various stocks.

From furnace 2| these cracked materials pass 6 through transfer line 38and pressure reduction valve 39 into evaporator 40 which is shownintegral with bubble tower 4| and separated therefrom by trap-out plate42. Tar is removed from and line 20, from which it passes through hotloil 5 pump 31 and is introduced into the coils of fur. nace 2| aspreviously indicated.

In place of having separate evaporators and bubble towers for theproducts from catalyst chamber 30 and furnace 2|, products from furnace2| can be passed from line 38 through shutolf valves 45a and 45h andpressure reduction valve 45e into line 3| and thence into evaporator 32.In this case evaporator 40 and bubble tower 4| with accompanyingequipment are not required. The mixed cycle stocks will leave by line 36and enter furnace 2| together, just as whenseparate towers areprovided.

Returning now to viscosity breaker furnace 28, it will be seen that thecracked material from this operation passes through transfer line 46into evaporator 41 which is integral'with bubble tower 48 and separatedtherefrom by trap-out plate 49. From the base of evaporator 41 tar isremoved by means of valved line 50 while from trap-out plate W't thebase of bubble tower 48 a gas oil cycle stock is removed by means ofvalve 5| and cycled via lines 52 and 23 and hot oil pump 24 lto thecoils of catalytic cracking furnace 25.

From bubble towers 33, 4| and 48 materials lighter than gas oil, whichconsist generally of gasoline range hydrocarbons and lighter materials,pass overhead through lines 53, 54 and 55, respectively, and thencethrough condensers 56, 51 and 58, respectively, and lines 59, 60 and 6|.respectively, to reflux drums 62, 63 and 64, respectively. The gasesfrom these various reflux drums are taken overhead through valves 65, 66and 61 and line 68 to compressors 69 from which they pass to stabilizerl2. Any gases which are already at pressures as high as that ofstabilizer I2 can, of course, be luy-passed around compressors 69.

Condensate from reflux drums 62, 63. and 64- is removed through pumps10, 1| and 12 respectively, and a portion is returned to the appropriatebubble tower by means of valves 13, 14 and .15, respectively, and lines16, 11 and 18, respectively. The remainder of this condensate passesthrough valves 19, and 8|, respectively, and thence through line 82 intostabilizer l2.

Stabilizer l2 is operated at an elevated pressure in the conventionalmanner. It is equipped with a reboiler which includes the conventionaltrap-out plate 83 and heater 84. The stabilizer is also provided withreflux and the pressure, reboiling and reflux are controlled to takestabilized gasoline olf the base of the tower through valved line 65 forstorage, further treatment or use.

Gases eliminated in producing stabilized gasoline pass overhead fromstabilizer I2 through line 86 and condenser 81 and thence to reuxV drum88. Condenser 81 is operated to condense such portion of the four carbonatom hydrocarbons as cannot be utilized in the finished gasolinetogether with a considerable amount of three carbon atom hydrocarbons.This condensate is removed from 5 the base of reflux drum 88 by means ofpump 88 and a portion of it is returned to stabilizer I2 as refluxthrough valve 80 and line 8|. The remainder is removed from the systemthrough valved line 92 for storage and use. Light gases gre removed fromthe system through valved line It will thus be seen that my newcombination cracking operation involves the separation of a crude oil orreduced crude oil into fractions comprising a heavy naphtha which iscracked thergas oil charging stock which is once-through basis and fromthe thermal cracking breaker y manner as to give only a very lightcracking, the

gas oil produced is not far removed in characteristics from virgin gasoil and thus constitutes a particularly suitable charging stock for thecatalytic cracking operation.

The iiow diagram of my combination cracking process as well as thedescription of it is highly simplied and various detailsL such forinstance as heat exchangers; pressure, temperature-and 4iiow controldevices; safety devices; stripping towers for trap-out streams;4additional valves and pumps;I insulation; to detail these featureswould add nothing to the knowledge oi those skilled in the art andwouldmerely serve to encumber this specification unnecessarily.

While my invention has been described in connection with aspeciiicembodiment thereof, it is to be understood that this can be modifiedetc., are omitted since in various ways and that I do not mean to belim- 3 ited thereby but only to the scope of the appended claims whichshould beconstrued as broadly as the prior art will permit.

I claim:

l. A combination cracking process comprising separating a crudepetroleum oil into fractions including a heavynaphtha fraction, a virgingas oil fraction and a residuum fraction, subjecting said gas oilfraction to a catalytic cracking operation, separating the products ofsaid cati alytic cracking operation into fractions including a gasolinefraction and a gas oil cycle stock fraction, subjecting said gas oilcycle stock fraction together with said heavy naphtha fraction to anon-catalytic thermal cracking operation, separating the products ofsaid thermal cracking operation into fractions which include a gasolinefraction and another gas oil cycle stock fraction, 'recycling said lastmentioned gas oil cycle stock fraction to said thermal crackingoperation, subjecting said residuum to a non-catalytic viscosity breakeroperation, separating the products of said viscosity breaker operationinto fractions includingl a' cleancycle stock fraction, and recyclingsaid clean cycle stock fraction to said ceatalytic cracking operation.

2. The method of increasing the efficiency of a combination thermal andcatalytic cracking system for the manufacture of high quality gasolinewhich method comprises fractionating a hydrocarbon charging stock in theabsence of crackedproducts to obtain a gas-oil fraction and aheavier-than-gas-oil fraction, passing the heavier-than-gas-oil fractionto a viscosity breaking system and heating it therein to a temperatureof about 825 tov 975 F. at a pressure of about 100 to 1000 pounds persquare inch, passing gas-oil from the products of the viscosity'breaking step in admixture with gas-oil from said first fractionatingstep through a catalytic cracking chamber at a temperature of about 800F. to 975 F. and a pressure oi about atmospheric to pounds per squareinch in the presence of a cracking catalyst, passing gas-oil from theproducts of catalytic crackingtogether with heavy' naphtha from saidirst-named fractionating means to a thermal cracking zone, maintaining apressure of about 100 to 1500 pounds per square inch and a temperatureof about 875 F. to 1100 F., fractionating the products from the thermalcracking zone in the absence of products from the catalytic cracking andviscosity breaking steps, returning gas-oil from the thermal crackingfractionating step Ato said thermal cracking zone and blending thegasoline obtained from said-first fractionating step, said catalyticcracking step, said viscosity breaking step and said thermal crackingfractionating step, respectively.

ERNEST W. THIELE.

